Half the world's spam comes from just 50 ISPs

Just 50 ISPs are responsible for the bulk of the world's spam, a new study shows, bringing hope that it might be a little easier than expected to wipe out some of the world's most prolific botnets.

The study, carried out for the Organization for Economic Cooperation and Development (OECD), gathered 109 billion spam messages between 2005 and 2009, emanating from 170 million unique IP addresses.

The researchers found that between 80 and 90 percent of spam arrived from an infected machine. Surprisingly, though, the networks of just 50 ISPs were found to account for half of all infections worldwide.

"To put it differently: the number of actors needed to create an impact on botnets is smaller than expected," says the report.